Field of the Invention
The present invention relates to a transmission mechanism.
Description of the Related Art
As a transmission mechanism for vehicle, a constant-mesh type transmission mechanism has been known. Patent Document 1 discloses a constant-mesh type transmission mechanism including two shafts: a counter shaft and a drive shaft. In such transmission mechanism, a plurality of driving gears are disposed on the counter shaft where rotative power is transmitted from a crankshaft, and a plurality of driven gears are disposed on the drive shaft that outputs the rotative power. Each of the plurality of driving gears is constantly engaged with each of the plurality of driven gears. Then, changing a transmission route of the rotative power from the counter shaft to the drive shaft shifts gears.
A six-speed is widely used for such constant-mesh type transmission mechanism. However, a further multistage is required in order to ensure both improvement of fuel efficiency during high-speed running and securement of acceleration performance during acceleration. As a configuration to ensure the multistage of the constant-mesh type transmission mechanism, Patent Document 2 discloses a configuration that adds a two-speed auxiliary transmission mechanism to a five-speed main transmission mechanism.
Patent Document 1: Japanese Laid-open Patent Publication No. 2005-127392
Patent Document 2: Japanese Laid-open Patent Publication No. 61-189347
However, in the configuration that adds the auxiliary transmission mechanism, it is necessary to add a rotation shaft for adjusting a rotation direction of the output rotative power and a mechanism for operating the auxiliary transmission mechanism, thus the configuration becomes complicated. On the other hand, in order to ensure the further multistage in the transmission mechanism including the two shafts: the counter shaft and the drive shaft, it is necessary to increase the number of the driving gears disposed on the counter shaft and the number of the driven gears disposed on the drive shaft. Therefore, it is necessary to extend the counter shaft and the drive shaft, thus deflections at center portions in longitudinal directions of the counter shaft and the drive shaft become large.